Which Keratometer is Most Reliable for Correcting Astigmatism with Toric Intraocular Lenses?

Purpose

To evaluate the accuracy of preoperative keratometers used in cataract surgery with toric intraocular lens (IOL).

Methods

Twenty-five eyes received an AcrySof toric IOL implantation. Four different keratometric methods, a manual keratometer, an IOL master, a Pentacam and an auto keratometer, were performed preoperatively in order to evaluate preexisting corneal astigmatism. Differences between the true residual astigmatism and the anticipated residual astigmatism (keratometric error) were compared at one and three months after surgery by using a separate vector analysis to identify the keratometric method that provided the highest accuracy for astigmatism control.

Results

The mean keratomeric error was 0.52 diopters (0.17-1.17) for the manual keratometer, 0.62 (0-1.31) for the IOL master, 0.69 (0.08-1.92) for the Pentacam, and 0.59 (0.08-0.94) for the auto keratometer. The manual keratometer was the most accurate, although there was no significant difference between the keratometers (p > 0.05). All of the keratometers achieved an average keratometric error of less than one diopter.

Conclusions

Manual keratometry was the most accurate of the four methods evaluated, although the other techniques were equally satisfactory in determining corneal astigmatism.     

Toric IOL positioning with a no-touch head-up display axis alignment

To compare a new no-touch alignment technique for toric intraocular lenses (IOL) with the conventional technique that uses a manual pendulum. In this retro     

Treatment of keratoconus by toric foldable intraocular lenses

PURPOSE: To report on the correction of marked regular corneal astigmatism due to keratoconus by toric intraocular lenses (IOL). SETTING: University eye hospital. METHODS: A 66-year-old woman presented with cataract and unilateral keratoconus (keratometric readings: 50.2/41.3 diopters [D]). She underwent routine cataract surgery with implantation of a foldable posterior chamber toric IOL (refractive power: +10.0 D sphere/+12.0 D cylinder). A 68-year-old surgically aphakic woman presented with peripheral accentuated keratoconus with regular and stable corneal astigmatism (keratometric readings: 39.75/61.5 D). She underwent secondary implantation of a foldable toric IOL (refractive power: -9.0 D sphere/+30.0 D cylinder) into the ciliary sulcus. RESULTS: After a follow-up period of 4 months, visual acuity increased to 0.70 with a correction of +0.75 sphere -2.5 cylinder/84 degrees in Patient 1; after a follow-up period of 6 months, visual acuity increased to 0.60 with a correction of +1.0 -2.0/90 degrees in Patient 2. CONCLUSIONS: Foldable toric silicone IOL may be a surgical option in the management of regular marked corneal astigmatism caused by keratoconus.     

Accuracy and predictability of intraocular lens power calculation after laser in situ keratomileusis

PURPOSE: To study the accuracy and predictability of intraocular lens (IOL) power calculation in eyes that had laser in situ keratomileusis (LASIK). SETTING: Gimbel Eye Centre, Calgary, Alberta, Canada. METHODS: Refractive outcomes in 6 cataract surgery and lensectomy eyes after previous LASIK were analyzed retrospectively. Target refractions based on measured and refraction-derived keratometric values were compared with postoperative achieved refractions. Differences between target refractions calculated using 5 IOL formulas and 2 A-constants and achieved refractions were also compared. RESULTS: The refractive error of IOL power calculation in postoperative LASIK eyes was significantly reduced when refraction-derived keratometric values were used for IOL power calculation. Persistent residual hyperopia still occurred in some cases; this was corrected by hyperopic LASIK. Refractive results appeared more accurate and predictable when the Holladay 2 or Binkhorst 2 formula was used for IOL power calculation. CONCLUSION: Hyperopic error after cataract surgery in post-LASIK eyes was significantly reduced by using refraction-derived keratometric values for IOL power calculation. Persistent hyperopic error was corrected by hyperopic LASIK.     

Astigmatism correction with a foldable toric intraocular lens in cataract patients

PURPOSE: To determine the efficacy and rotational stability of a toric posterior chamber silicone intraocular lens (IOL) to correct preoperative astigmatism in cataract patients. SETTING: Department of Ophthalmology, University Hospital of Vienna, Vienna Austria. METHODS: Between 1993 and 1998, foldable toric single-piece plate-haptic silicone IOLs were implanted in 37 eyes (30 patients). The cylindrical IOL power was 2.00 diopters (D) (n = 29), 3.50 D (n = 7), or 4.00 D (n = 1). Phacoemulsification was performed through a scleral or a corneal sutureless self-sealing incision. Outcomes of Snellen visual acuity (without, with spherical, and with best correction), refractive and keratometric astigmatism, and IOL rotation after early postoperative (mean 15.9 days +/- 10.1 [SD]) and long-term (mean 20.3 +/- 16.6 months) follow-ups were evaluated. RESULTS: At last follow-up, 31 eyes (83.8%) had a spherically corrected and 34 (91.9%) a best corrected visual acuity of 0.5 (20/40) or better. Mean preoperative refractive and keratometric astigmatism was 2.68 and 2.70 D, respectively. At the last postoperative follow-up, mean refractive astigmatism was reduced to 0.84 D; keratometric astigmatism was 2.30 D. In 7 eyes (18.9%), the IOL axis was rotated a maximum of 25 degrees. In all 37 eyes, the axis of the toric IOL remained within 30 degrees of rotation. CONCLUSIONS: Early postoperative and long-term follow-ups showed effective and stable correction of astigmatism after implantation of a foldable toric posterior chamber silicone IOL.     

Multicenter biometry study of 1 pair of eyes.

PURPOSE: To assess the accuracy of biometry for intraocular lens (IOL) power calculation. SETTING: Six ophthalmic surgery centers in Europe and 1 in the United States. METHODS: Biometry was done as if in preparation for cataract surgery in 2 eyes of the same person with 10 combinations of operator and instrument. Data analysis followed a standardized procedure to assess repeatability (within-center variability) and reproducibility (between-center variability) of the test methods. RESULTS: The reproducibility of the corneal radius measurement was 0.06 mm. The use of different keratometric indices made conversion to K-values less reliable. The repeatability of the axial length (AL) measurement of 0.30 mm and the reproducibility of 0.66 mm converted to a calculated IOL power of 0.75 diopter (D) and 1.65 D, respectively. Thus, this potential patient runs the risk of a refractive surprise of up to 1.10 D purely as a result of a measurement error within a center and up to 2.30 D if the patient goes to the worst-case center. CONCLUSIONS: The biometry results show that the measured corneal radius can be used with confidence. Reproducibility errors in AL determination require personalization of formula constants or correction at the source by proper calibration.     

Accuracy and predictability of intraocular lens power calculation after photorefractive keratectomy

PURPOSE: To investigate the accuracy and predictability of intraocular lens (IOL) power calculation in postoperative photorefractive keratectomy (PRK) eyes. SETTING: Gimbel Eye Centre, Calgary, Alberta, Canada. METHODS: The results in 5 cataract surgery eyes that had had PRK were analyzed retrospectively. Target refractions based on actual and refraction-derived keratometric values were compared with postoperative achieved refractions. The target refractions calculated using 5 IOL formulas and 2 A-constants were also compared with the achieved refractions. RESULTS: In postoperative PRK eyes, the power calculation was more accurate and predictable when the smaller of either the actual or refraction-derived keratometric value was used to calculate the IOL power. The difference between target and achieved refractions appeared smaller when the Binkhorst formula was used. No significant hyperopic shift was observed after cataract surgery. CONCLUSION: The smaller of the actual or the refraction-derived keratometric value is recommended for calculating IOL power in post-PRK eyes.     

Intraocular lens power calculation in high myopic eyes with previous radial keratotomy

PURPOSE: To determine an accurate method of intraocular lens (IOL) power calculation in highly myopic eyes with previous radial keratotomy (RK). METHODS: Five eyes that had undergone RK with preoperative myopia >-14.0 diopters (D) were studied retrospectively. The keratometric values obtained with the clinical history method, contact lens over-refraction method, conventional keratometry, adjusted keratometry, and Orbscan II were compared to the true keratometric value calculated retrospectively with the SRK/T formula. RESULTS: The true keratometric value was closest to that from the contact lens over-refraction method in one eye and to the flatter keratometric value between simulated keratometry (Sim K) and the 3-mm diameter central zone mean keratometric value obtained with axial keratometric power map of Orbscan II in four eyes. CONCLUSIONS: The flatter keratometric value between Sim K and the 3-mm zone mean keratometric value from Orbscan II was closest to the true postoperative RK keratometric value of the central cornea.     

Verion导航与手动标记对Toric人工晶状体植入术后角膜散光矫正的影响

目的：比较Verion导航系统与手动标记对散光矫正型人工晶状体（Toric IOL）植入术矫正角膜散光效果的影响。方法：前瞻性随机对照研究。选取2015 年2 月至2017 年2 月在江苏省常州市第三人民医院就诊的白内障合并规则性角膜散光> 1.0 D的患者80例（80眼）。使用随机数字表法将患者随机分配到观察组（40例）和对照组（40例）。观察组使用Verion数字导航系统引导术中Toric IOL的植入，对照组术前在裂隙灯显微镜下手动标记用于指导Toric IOL的植入。2 组患者均行超声乳化白内障吸除联 合Toric IOL植入术，观察患者术前及术后3个月的裸眼远视力（UCDVA）（ LogMAR）、最佳矫正远视力（BCDVA）（ LogMAR）、角膜散光以及术后3个月的实际与预期残余散光、Toric IOL轴位。计量资料组间比较采用独立样本t检验，计数资料组间比较采用卡方检验。结果：对照组术后平均UCDVA为0.13±0.13，观察组术后平均UCDVA为0.11±0.11，2 组间差异无统计学意义（t=-0.96，P=0.34）。实际与预期残余散光的偏差绝对值对照组为（0.21±0.12）D，观察组为（0.12±0.11）D，2 组间差异有统计学意义（t=-3.71，P=0.001）。术后对照组裂隙灯显微镜下Toric IOL实际轴位与预期安放轴位偏差绝对值为4.6°±3.0°，观察组为2.2°±1.6°，2组间差异有统计学意义（t=-3.69，P=0.001）。结论：在Toric IOL植入术中应用Verion数字导航系统相较于传统手动标记技术可明显减小术后实际与预期散光的差值，减少术后Toric IOL轴位与预期轴位的偏离。     

Visual acuity improvements after implantation of toric intraocular lenses in cataract patients with astigmatism: A systematic review

ABSTRACT: BACKGROUND: Cataracts are a common and significant cause of visual impairment globally. We aimed to evaluate uncorrected distance visual acuity (UDVA) as an outcome in treating astigmatic cataract patients to assist clinicians or ophthalmologists in their decision making process regarding available interventions. RESULTS: The systematic review identified 11 studies which reported UCVA. All 11 studies reported UDVA. Four brands of toric intraocular lenses (IOLs) were reported in these studies. All studies identified in the literature search reported improvements in UDVA following surgical implant of a toric IOL. The largest improvements in VA were reported using the Human Optics MicroSil toric IOL (0.74 LogMAR, UDVA) and the smallest improvements were also reported using the Human Optics MicroSil toric IOL (0.23 LogMAR, UDVA) in a different study. CONCLUSIONS: The results of this systematic review showed the aggregate of studies reporting a beneficial increase in UDVA with the use of toric IOLs in cataract patients with astigmatism.     

Intraocular lens power calculation after keratorefractive surgery

The number of keratorefractive procedures designed to correct refractive errors has dramatically increased over the last few years. The techniques for cataract extraction and intraocular lens implantation have evolved into a refractive surgical procedure as well as an operation to improve best corrected visual acuity and/or spectacle independence. The calculation of intraocular lens power for a desired refractive target can be challenging in post-refractive surgically treated eyes, given the frequent case reports of "refractive surprises" after cataract surgery. After corneal refractive surgery, the direct use of the measured topographic or keratometric values, with no correction, results in less accurate calculation of intraocular lens (IOL) power required for cataract surgery than calculation in virgin eyes. After laser refractive surgery for myopia, this could result in an overestimation of the corneal power and subsequent underestimation of the IOL power, therefore leading to a hyperopic outcome after phacoemulsification. Conversely, after laser refractive surgery for hyperopia, inaccuracy in the keratometric power estimation could result in a myopic outcome after phacoemulsification. Despite current progress in this subject, awareness of the shortcomings of classical methods and suggested strategies to improve accuracy can be valuable to clinicians. This article provides an overview of the possible sources of error in intraocular lens power calculation in post-keratorefractive patients, and reviews the methods to minimize intraocular lens power errors.     

Changes in keratometric corneal power and refractive error after laser thermal keratoplasty

PURPOSE: To evaluate the effect of laser thermal keratoplasty (LTK) on corneal power and refractive error to develop a logical approach to calculating accurate intraocular lens (IOL) power for cataract surgery. SETTING: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. METHODS: Laser thermal keratoplasty was performed in 27 eyes of 23 patients. Preoperatively and postoperatively, the refractive error was measured and the corneal power obtained by manual keratometry and topography. The changes in keratometric corneal power and refractive error after LTK were compared. RESULTS: The mean age of the 15 women and 8 men was 45.0 years +/- 4.6 (SD) (range 43 to 61 years). The mean preoperative refractive error was +1.43 +/- 0.97 diopters (D) (range 0 to +3.63 D) at the spectacle plane and +1.46 +/- 1.01 D (range 0 to +3.79 D) at the corneal plane. The mean postoperative refractive error was -0.44 +/- 1.07 D (range -2.24 to +2.18 D) at the spectacle plane and -0.44 +/- 1.08 D (range -2.18 to +2.23 D) at the corneal plane. After surgery, corneal powers measured by manual keratometry were significantly smaller than those measured by topography (P<.001) and refractive error changes were significantly smaller than keratometric changes (P<.001). CONCLUSIONS: After LTK, corneal power measured by manual keratometry was smaller than that measured by corneal topography and changes in corneal power measured by conventional keratometric instruments were greater than changes in refractive error. This difference should be considered in calculating IOL power in post-LTK eyes to prevent undesirable hyperopia after cataract surgery.     

Acrysof toric人工晶状体的临床应用研究

目的 评价白内障术中植入一片式散光型人工晶状体(IOL)矫正术前角膜散光的疗效和旋转稳定性.方法 白内障超声乳化吸除联合Acrysof toric IOL植入31只眼,其中T3(柱镜为1.50D)19只眼,T4(柱镜为2.25D)7只眼,T5(柱镜为3.00 D)5只眼.另外,对照组30只眼,手术方式相同,术中植入SA60AT型IOL.白内障超声乳化吸除联合IOL植入手术通过颞侧角膜切口进行.观察术后早期(1周)和远期(3月)术眼散光和角膜散光,晶状体的旋转度数,裸眼视力(UCVA),球镜矫正视力(SCVA)和最佳矫正视力(BCVA).结果 在最后随访时,观察组全部患眼的UCVA均LogMAR 0.3(20/40)以上,而对照组有86.7%的患眼达到LogMAR0.3(20/40)以上.平均眼散光观察组为(0.44±0.24)D,对照组为(1.44±0.34)D.观察组有21只眼(77%)的IOL轴旋转小于3°,所有患眼IOL旋转不超过9°.结论 术后早期和远期观察表明Acrysof toric IOL,植入可以有效和稳定地矫正白内障患者术前即存在的散光.     

Long-Term Efficacy and Rotational Stability of AcrySof Toric Intraocular Lens Implantation in Cataract Surgery

Purpose

To evaluate the long-term efficacy and rotational stability of the AcrySof toric intraocular lens (IOL) in correcting preoperative astigmatism in cataract patients.

Methods

This prospective observational study included 30 eyes from 24 consecutive patients who underwent implantation of an AcrySof toric IOL with micro-coaxial cataract surgery between May 2008 and September 2008. Outcomes of visual acuity, refractive and keratometric astigmatism, and IOL rotation after 1 day, 1 month, 3 months, and long-term (mean, 13.3±5.0 months) follow-up were evaluated.

Results

At final follow-up, 73.3% of eyes showed an uncorrected visual acuity of 20/25 or better. The postoperative keratometric value was not different from the preoperative value; mean refractive astigmatism was reduced to -0.28±0.38 diopter (D) from -1.28±0.48 D. The mean rotation of the toric IOL was 3.45±3.39 degrees at final follow-up. One eye (3.3%) exhibited IOL rotation of 10.3 degrees, the remaining eyes (96.7%) had IOL rotation of less than 10 degrees.

Conclusions

Early postoperative and long-term follow-up showed that implantation of the AcrySof toric IOL is an effective, safe, and predictable method for managing corneal astigmatism in cataract patients.     

Error induced by the estimation of the corneal power and the effective lens position with a rotationally asymmetric refractive multifocal intraocular lens

AIM:To evaluate the prediction error in intraocular lens (IOL) power calculation for a rotationally asymmetric refractive multifocal IOL and the impact on this error of the optimization of the keratometric estimation of the corneal power and the prediction of the effective lens position (ELP).METHODS:Retrospective study including a total of 25 eyes of 13 patients (age, 50 to 83y) with previous cataract surgery with implantation of the Lentis Mplus LS-312 IOL (Oculentis GmbH, Germany). In all cases, an adjusted IOL power (PIOLadj) was calculated based on Gaussian optics using a variable keratometric index value (nkadj) for the estimation of the corneal power (Pkadj) and on a new value for ELP (ELPadj) obtained by multiple regression analysis. This PIOLadj was compared with the IOL power implanted (PIOLReal) and the value proposed by three conventional formulas (Haigis, Hoffer Q and Holladay Ⅰ).RESULTS:PIOLReal was not significantly different than PIOLadj and Holladay IOL power (P>0.05). In the Bland and Altman analysis, PIOLadj showed lower mean difference (-0.07 D) and limits of agreement (of 1.47 and -1.61 D) when compared to PIOLReal than the IOL power value obtained with the Holladay formula. Furthermore, ELPadj was significantly lower than ELP calculated with other conventional formulas (P<0.01) and was found to be dependent on axial length, anterior chamber depth and Pkadj.CONCLUSION:Refractive outcomes after cataract surgery with implantation of the multifocal IOL Lentis Mplus LS-312 can be optimized by minimizing the keratometric error and by estimating ELP using a mathematical expression dependent on anatomical factors.     

Evaluation of a toric intraocular lens with a Z-haptic

PURPOSE: To evaluate the efficacy and rotational stability of the MicroSil 6116TU foldable 3-piece silicone toric intraocular lens (IOL) (HumanOptics). SETTING: Department of Ophthalmology, Hillingdon Hospital, Uxbridge, Middlesex, United Kingdom. METHODS: This prospective observational study included 21 eyes of 14 consecutive patients with more than 1.50 diopters (D) of preexisting corneal astigmatism having cataract surgery. Phacoemulsification was performed, and a MicroSil 6116TU toric IOL was inserted through a 3.4 mm temporal corneal incision. LogMAR uncorrected visual acuity (UCVA), best corrected visual acuity, refraction, keratometry, and cylinder axis of the toric IOL were measured. RESULTS: The mean preoperative refractive and keratometric astigmatism was 3.52 D +/- 1.11 (SD) and 3.08 +/- 0.76 D, respectively. Six months postoperatively, the logMAR UCVA in eyes without ocular comorbidity (n = 14) was 0.20 +/- 0.15 (Snellen 20/32). Seventy-nine percent (11 eyes) had a visual acuity of 0.24 (Snellen 20/35) or better. The mean refractive astigmatism at 6 months was 1.23 +/- 0.90 D. Vector analysis using the Holladay-Cravy-Koch method showed a mean reduction in refractive astigmatism of 2.16 +/- 2.33 D. The mean difference between intended and achieved cylinder axis at 6 months was 5.2 degrees (range 0 to 15 degrees). No IOL rotated more than 5 degrees during the follow-up period. CONCLUSIONS: The MicroSil 6116TU toric IOL reduced visually significant keratometric astigmatism and increased spectacle independence. The IOL was stable in the capsular bag, showing no significant rotation up to 6 months postoperatively.     

Effects of posterior corneal astigmatism on the accuracy of AcrySof toric intraocular lens astigmatism correction

AIM: To evaluate the effects of posterior corneal surface measurements on the accuracy of total estimated corneal astigmatism. METHODS: Fifty-seven patients with toric intraocular lens (IOL) implantation and posterior corneal astigmatism exceeding 0.5 diopter were enrolled in this retrospective study. The keratometric astigmatism (KA) and total corneal astigmatism (TA) were measured using a Pentacam rotating Scheimpflug camera to assess the outcomes of AcrySof IOL implantation. Toric IOLs were evaluated in 26 eyes using KA measurements and in 31 eyes using TA measurements. Preoperative corneal astigmatism and postoperative refractive astigmatism were recorded for statistical analysis. The cylindrical power of toric IOLs was estimated in all eyes. RESULTS: In all cases, the difference of toric IOL astigmatism magnitude between KA and TA measurements for the estimation of preoperative corneal astigmatism was statistically significant. Of a total of 57 cases, the 50.88% decreased from Tn to Tn-1, and 10.53% decreased from Tn to Tn-2. In all cases, 5.26% increased from Tn to Tn+1. The mean postoperative astigmatism within the TA group was significantly lower than that in the KA group. CONCLUSION: The accuracy of total corneal astigmatism calculations and the efficacy of toric IOL correction can be enhanced by measuring both the anterior and posterior corneal surfaces using a Pentacam rotating Scheimpflug camera.     

Refractive error in cataract surgery after previous refractive surgery

Bilateral cataract extraction with posterior chamber intraocular lens (IOL) implantation was performed in a patient after previous photorefractive keratectomy, radial keratotomy (RK) combined with astigmatic keratotomy, and retreatment of RK. Significant hyperopic error was observed after cataract surgery, and the IOLs were eventually exchanged in both eyes. A review of this case found that the refractive error was smaller when a refraction-derived keratometric value was selected for IOL power calculation. Nevertheless, hyperopic error still occurred.     

Intraocular lens power calculation in eyes after corneal refractive surgery

PURPOSE: The purpose of this review article is to discuss the major reasons for postoperative hyperopia after cataract surgery following radial keratotomy (RK) and photorefractive keratectomy (PRK) and to illustrate potential methods for improvement of intraocular lens (IOL) power prediction after keratorefractive surgery based on exemplary model calculations. METHODS: We previously performed model calculations in eyes after PRK for myopia (-1.50 to -8.00 D, mean -5.40 +/- 1.90 D) using keratometry readings as measured by the Zeiss keratometer and the TMS-1 topography unit and as calculated using the "clinical history method" (spherical equivalent refraction change) and change in anterior surface keratometry readings. RESULTS: We found that after PRK, mean measured keratometry readings were significantly greater than respective calculated values considering the preoperative to postoperative change of anterior corneal surface (P < .001), which itself was significantly greater than calculated keratometry readings considering the preoperative to postoperative change of spherical equivalent refraction (P < .001). IOL power underestimation correlated significantly with the difference between preoperative and postoperative spherical equivalent refraction (P = .001). CONCLUSIONS: For correct assessment of keratometric readings to be entered into more than one modern third-generation IOL power calculation formula (but not a regression formula), the clinical history method should be applied whenever refraction and keratometric diopters before the keratorefractive procedure are available to the cataract surgeon. If preoperative keratometric diopters and refraction are not known, average central power on the postoperative videokeratograph may be used after RK, but refined calculation of keratometric diopters from radius of anterior and posterior corneal surface should be used after PRK and/or LASIK.     

Challenges and approaches in modern biometry and IOL calculation

The introduction of new intraocular lenses (IOLs), industry marketing to the public and patient expectations has warranted increased accuracy of IOL power calculations. Toric IOLs, multifocal IOLs, aspheric IOLs, phakic lenses, accommodative lenses, cases of refractive lens exchange and eyes that have undergone previous refractive surgery all require improved clinical measurements and IOL prediction formulas. Hence, measurement techniques and IOL calculation formulas are essential factors that affect the refractive outcome.Measurement with ultrasound has been the historic standard for measurement of ocular parameters for IOL calculation. However the introduction of optical biometry using partial coherence interferometry (PCI) has steadily established itself as the new standard. Additionally, modern optical instruments such as Scheimpflug cameras and optical coherence tomographers are being used to determine corneal power that was normally the purview of manual keratometry and topography.A number of methods are available to determine the IOL power including the empirical, analytical, numerical or combined methods. Ray tracing techniques or paraxial approximation by matrix methods or classical analytical ‘IOL formulas’ are actively used in for the prediction of IOL power. There is no universal formula for all cases – phakic and pseudophakic cases require different approaches, as do short eyes, long eyes, astigmatic eyes or post-refractive surgery eyes. Invariably, IOLs are characterized by different methods and lens constants, which require individual optimization. This review describes the current methods for biometry and IOL calculation.